Protein serine/threonine phosphatase inhibitors suppress phenobarbital-induced Cyp2b10 gene transcription in mouse primary hepatocytes.
Using a primary hepatocyte culture in which the mouse Cyp2b10 gene transcription is activated by phenobarbital (PB)-type inducers, we examined the cellular signalling mechanisms associated with PB induction. Low nanomolar concentrations of protein serine/threonine phosphatase inhibitors okadaic acid (OA) and calyculin A blocked the induction of CYP2B10 mRNA. Nuclear run-on assays indicated that OA suppressed Cyp2b10 gene transcription. Pretreatment of the cells with an inhibitor of Ca2+/calmodulin-dependent protein kinases ¿1-[N, O-bis-(5-isoquinolinesulphonyl)-N-methyl-L-tyrosyl]-4- phenylpiperazine (KN-62)¿ or with a flavonoid, naringin, were completely or partly protective respectively against the OA-mediated suppression of CYP2B10 mRNA. Several other established modulators of protein kinase activities did not greatly affect the induction of CYP2B10 mRNA, nor could they prevent the suppressive effect of OA. Our results indicate that specific protein phosphorylation-dephosphorylation is required for the induction of Cyp2b10 gene expression, which is modulated through multiple endogenous and exogenous signals.
Honkakoski
P
P
Department of Pharmaceutics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland.
Negishi
M
M
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008810:Mice, Inbred C57BL; D019319:Okadaic Acid / Q000494:pharmacology; D010634:Phenobarbital / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D012333:RNA, Messenger / Q000378:metabolism; D013250:Steroid Hydroxylases; D014158:Transcription, Genetic / Q000187:drug effects*
D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D019319:Okadaic Acid; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C101679:Cyp2b10 protein, mouse; D000072467:Cytochrome P450 Family 2; D010749:Phosphoprotein Phosphatases; D010634:Phenobarbital